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Alaska’s Ice Drain 2004-07

Published: February 26th, 2010

Audio Commentary

Alaska has only about 5% of the total ice Greenland has — but from 2004 to 2007, Alaska shed an average of 80 billion metric tons per ear, under half the amount that Greenland did. Put another way, relative to its own stock, Alaska is losing ice about eight times faster than Greenland.

This trend especially concerns scientists because meltwater and ice emptying into the oceans raise global sea level. Currently, sea level is increasing at about 1.25 inches per decade, and researchers estimate that, globally, glaciers and ice caps — among which Alaska is making the biggest contribution — are contributing perhaps over 20% of this rate.

Why is Alaska losing ice? It appears linked in several ways to climate warming, which is strongest in the Arctic. First, surface melt of ice has been increasing. Second, much of the meltwater drains to the base of glaciers and then lubricates the glaciers’ flow toward the sea. And finally, where the glaciers plunge into the ocean, warmer water appears to be eroding the glacial tongues that help hold flow back.

How do we know Alaska has been losing ice? The best evidence comes from NASA’s GRACE satellite mission. GRACE has provided a direct measure of mass change through time, through its unique “scale in the sky” capabilities.

The calculations behind this graphic assume it is possible to pack 100 metric tons of ice per 60 feet of freight train length (the 60 feet composed of one car plus the space separating it on one side from the next car).

GRACE: Launched in March 2002, NASA’s Gravity Recovery and Climate Experiment mission (GRACE) deploys two satellites that orbit the Earth in tandem. The pair measure the distance separating each other to an accuracy of 1% of the width of a human hair — and they orbit as far apart as Washington, DC and Philadelphia. Because each satellite accelerates or decelerates depending on the mass of the area beneath it (for example, a massive mountain range vs. flat lowlands), and because one satellite trails the other at some distance, the record of the shifting distance between them can be read like a giant planetary scale. And since they orbit over the same areas every ten days, the GRACE satellites provide a detailed record of mass changes in time, even tracking the seasonal accumulation and melting of Arctic snow.